Field of the Invention
The present invention generally relates to cordless telephones and, more particularly, to a cordless telephone in which the power consumption of a battery can be reduced.
A cordless telephone available in the United States of America has 10 duplex channels, that is, channels 1-10, but does not have a control channel. Further, in Japan, a low power cordless telephone does not have a control channel. In the cordless telephone having no control channel, power consumption of a battery used in a handset unit may be reduced by a method proposed by persons having a duty to assign to the assignee of the present application, and which is generally illustrated in FIG. 1. Such method is particularly disclosed in U.S. patent application Ser. No. 07/621,846, filed Dec. 4, 1990, now abandoned.
More specifically, as shown in FIG. 1, a base unit (master station) is powered by a commercially available AC power source. In a standby mode, the first to tenth channels are sequentially received and monitored repeatedly while awaiting a connection request from the handset unit. The time necessary for detecting the connection request from the handset unit is approximately 120 milliseconds per channel. Accordingly, all the channels are scanned in a cycle of about 1.2 seconds.
In the standby mode, the handset unit (remote station) receives and monitors predetermined channels, for example, the third and seventh channels, for checking whether or not a connection request from the base unit was sent. If no such connection request is received, then the handset unit enters a sleep mode of, for example, about 3.5 seconds. This cycle is repeatedly performed by the handset unit.
Accordingly, the handset unit is placed in a sleep mode during most of the standby mode. Therefore, the battery power consumption is reduced.
The arrangement and operation of such cordless telephone will be described more fully hereinafter. In the following explanation, the channels that the handset unit receives and monitors in the standby mode are the third and seventh channels.
FIG. 2 shows the arrangement of the above mentioned cordless telephone system which is mainly composed of a handset unit 1, a base unit 2 and a telephone line network 3 (external line).
In the handset unit 1, reference numerals 110 and 120 designate a transmitting circuit and a receiving circuit, respectively. The transmitting circuit 110 converts a sound signal St and a command signal CMND (which will be explained more fully later) into an FM (frequency-modulated) up-channel signal Su and transmits the same. The receiving circuit 120 receives and demodulates an FM down-channel signal Sd to provide a sound signal Sr and the command signal CMND. Further, the receiving circuit 120 detects limiter noise generated from, for example, an intermediate frequency amplifier and, as a result, generates a detection signal SQLC which indicates the presence or absence of the FM down-channel signal Sd.
Further, in the handset unit 1, reference numerals 131 and 132 designate a dial key and a talk key, respectively, in which the talk key 132 is a non-lock type push switch. Each time the talk key 132 is depressed, the handset unit 1 is alternately changed between the standby mode and the talk mode. In the standby mode, the handset unit 1 is set for making an outgoing call from the handset unit 1, and the handset unit 1 intermittently receives two channels, in this case, the third and seventh channels as shown in FIG. 1, and awaits a connection request from the base unit 2. In the talk mode, the handset unit 1 performs continuous reception and transmission between itself and the base unit 2.
Reference numerals 133 to 137 designate auxiliary keys such as a hold key and the like which may be formed of non-lock type push switches. Reference numeral 139 designates a speaker used for a ringer. A microcomputer 140 controls the entire system of the handset unit 1 and may, for example, be a one-chip type general-purpose microcomputer, such as Model No. .mu.PD75108 manufactured by the NEC Corporation. The microcomputer 140 generates the command signal CMND which is transmitted by the transmitting circuit 110, and identifies the command signal CMND and the detection signal SQLC derived from the receiving circuit 120. Further, the microcomputer 140 generates control signals TCTL and RCTL that are used to respectively permit or inhibit the transmission and reception operations of the transmitting circuit 110 and the receiving circuit 120, to designate the channel and to perform muting.
Reference numerals 141 and 142 depict memories, that is, memory 141 is a read only memory (ROM) which stores therein a system identifying code SYID of 25 bits that is used to identify this cordless telephone from other cordless telephones. The memory 142 is a random access memory (RAM) for storing therein channel data CHDT which indicates the channel or channels which may be, received by the handset unit 1, for example, the third and seventh channels, in the standby mode.
Reference numeral 151 designates a battery which is preferably a rechargeable battery such as a nickel-cadmium battery. An output voltage signal from battery 151 is supplied to respective portions of the handset unit 1, thus providing the operation voltage. Reference numeral 161 depicts a light emitting diode (LED) which is used to indicate a hold state of the handset unit 1.
On the other hand, the base unit 2 includes a transmitting circuit 210 and a receiving circuit 220 which are substantially the same as the transmitting circuit 110 and the receiving circuit 120, respectively, of the handset unit 1. In the standby mode, the receiving circuit 220 awaits an incoming call from the telephone line network 3 and also is scanning all up-channels in order to receive a connection request from the handset unit 1 as shown in FIG. 1. In the talk mode, the base unit 2 performs continuous reception and transmission between itself and the handset unit 1.
Further, in the base unit 2, reference numerals 211, 221, 231, 232 and 239 designate a transmitter, a receiver, a dial key, a switch corresponding to a telephone hook switch and a speaker for a ringer respectively. Reference numerals 233 to 237 represent auxiliary keys, for example, a hold key, and may be formed of non-lock type push switches.
System control microcomputer 240 performs similar processings to those of the aforenoted microcomputer 140 and also controls the operation of the entire system of this cordless telephone. As with the microcomputer 140, the microcomputer 240 may be a one-chip type general-purpose microcomputer, such as Model No. .mu.PD75108 manufactured by the NEC Corporation. Reference numerals 241 and 242 designate memories which correspond to the memories 141 and 142, respectively. The ROM 241 stores therein the system identifying code SYID and the RAM 242 stores therein the data CHDT indicative of the channel or channels which the handset unit 1 receives and monitors.
Further, in the base unit 2, reference numerals 261, 262, 263 and 264 designate a two-line to four-line converting circuit, a switch circuit that corresponds to a hook switch of a standard telephone set, a generating circuit for generating a dial tone signal (i.e. a DTFM signal), and a detecting circuit for detecting a ring tone signal, respectively.
FIG. 3 shows an example of a signal format of the command signal CMND. This command signal CMND includes a bit synchronizing signal BSYN of 24 bits at the head thereof and a frame synchronizing signal FSYN of 16 bits. In this case, the bit synchronizing signal BSYN and the frame synchronizing signal FSYN have specific bit patterns which may be expressed as follows: EQU BSYN="101010 . . . 10" EQU FSYN="1100010011010110" . . . up-channel EQU FSYN="1001001100110110" . . . down-channel
Following the signal FSYN, the command signal CMND further includes a system identifying code SYID of 25 bits, an error correction code ECC of 12 bits for this system's identifying code SYID, a dummy bit DBIT of 3 bits and a control code CTRL of 5 bytes (40 bits), in this order.
In the control code CTRL of 5 bytes, the fist byte CTL1 is a code indicative of the control contents of the handset unit 1 and the base unit 2, and the second byte CTL2 to fifth byte CTL5 are parameters, data and so on associated with the first byte CTL1.
When the handset unit 1 or the base unit 2 receives the command signal CMND, the microcomputer 140 or 240 respectively determines whether or not the identifying code SYID in the command signal CMND coincides with the identifying code SYID stored in the ROM 141 or 241. When the respective identifying codes are coincident with each other, the command signal CMND is regarded as being valid, otherwise the command signal CMND is regarded as being invalid.
In the standby mode, the operations shown in FIG. 1 or the operations shown in the upper portions of FIGS. 4 to 6 are carried out.
More specifically, in FIGS. 4 to 6, the solid lines in the vertical direction represent the conditions, along a time direction, of the handset unit 1 and the base unit 2. As is to be appreciated, these solid lines in the vertical direction are not drawn to scale along the time axis direction. The single solid lines represent the sleep mode, the double solid lines represent a mode in which only reception is permitted and the double solid lines with the hatched portions represent periods in which transmission and reception are permitted.
The handset unit 1 alternately and intermittently receives and monitors the down third and seventh channels in accordance with the channel data CHDT stored in the RAM 142, while the base unit 2 repeatedly scans all up-channels.
An outgoing call from the handset unit 1 to the external line 3 is performed as in the connection sequence shown in FIG. 4.
More specifically, if talk key 132 is depressed while the handset unit 1 is set in the standby mode, the depression of the talk key 132 is detected by the microcomputer 140, whereby the receiving circuit 120 is made operative to receive the down third channel or the down seventh channel as indicated by the channel data CHDT stored in the RAM 142. That is, one of the above-mentioned channels, for example, the third channel is vacant, and the reception channel of the receiving circuit 120 is fixed to the down third channel and continuous reception is thereafter permitted. Further, the transmitting circuit 110 is permitted to transmit through the up third channel, thus placing the handset unit 1 in the talk mode on the third channel.
Subsequently, the command signal CMND whose control code CTRL indicates the request to the outgoing call is repeatedly supplied from the microcomputer 140 to the transmitting circuit 110, whereupon the command signal CMND is converted into the FM signal Su of the up third channel and transmitted to the base unit 2 via an antenna 100.
Then, in the base unit 2, the signal Su, which is in the form of radio waves, is received by an antenna 200 and supplied to receiving circuit 220. Concurrently therewith, the receiving circuit 220 is repeatedly scanning all up channels so that, when the reception channel becomes the third channel, the receiving circuit 220 senses the arrival of signal Su and, as a result, generates the detection signal SQLC. The scanning of the receiving circuit 220 is then stopped at the third channel, whereupon the receiving circuit 220 demodulates the FM signal Su so as to provide the command signal CMND. This command signal CMND is supplied to the microcomputer 240 which determines whether or not the identifying code SYID in the command signal CMND coincides with the identifying code SYID stored in the ROM 241.
In this case, since the identifying codes SYID are coincident with each other and the control code CTRL in the command signal CMND indicates the request of the outgoing call, the transmitting circuit 210 is permitted by the microcomputer 240 to transmit in the corresponding channel in which the FM signal Su is received, that is, the down third channel. Accordingly, the base unit 2 is also placed in the talk mode on the third channel.
A command signal CMND which answers the request of the outgoing call is then supplied from the microcomputer 240 to the transmitting circuit 210, whereupon the command signal CMND is converted into the FM signal Sd of the down third channel and transmitted to the handset unit 1 via the antenna 200.
The FM signal Sd transmitted from the base unit 2 to the handset unit 1 through the down third channel is received by the antenna 100 and supplied to the receiving circuit 120, whereby the command signal CMND is generated by the receiving circuit 120 and supplied to the microcomputer 140.
Since the identifying code SYID in the command signal CMND is coincident with the identifying code SYID stored in the ROM 141 and the control code CTRL in the command signal CMND indicates the answer to the request of the outgoing call, the talk modes of the transmitting circuit 110 and the receiving circuit 120 in the third channel are established.
Accordingly, the handset unit 1 and the base unit 2 are connected via the third channel.
Further, in the base unit 2, the switch circuit 262 is placed in the off hook mode, whereby the transmitting circuit 210 and the receiving circuit 220 are connected to the telephone lines network 3 via the converting circuit 261 and the switch circuit 262.
Therefore, the handset unit 1 is connected to the telephone line network 3 via the base unit 2.
The user may now input a telephone number of a party to be called by using the dial key 131 of the handset unit. As a result, the command signal CMND, whose control code CTRL indicates the transmission of a telephone number and the corresponding telephone number, is generated and converted into the up channel FM signal Su and transmitted.
Accordingly, in the base unit 2, the receiving circuit 220 receives the Su signal and generates the command signal CMND, in which the control code CTRL of this command signal CMND indicates the transmission of a telephone number and the corresponding telephone number. As a result, the generating circuit 263, which is controlled by the microcomputer 240 in accordance with the telephone number, generates a dial tone signal corresponding to the telephone number supplied thereto from the handset unit 1. This dial tone signal is transmitted through the converting circuit 261 and the switch circuit 262 to the telephone line network 3.
When the called phone is answered, an audio signal Sr from the party being called is supplied to the transmission circuit 210 via a signal line formed of the telephone line network 3, the switch circuit 262 and the converting circuit 261, in that order. This audio signal Sr is thereon converted into the FM down channel signal Sd and transmitted by way of the antenna 200.
This signal Sd is received by way of antenna 100 of the handset unit 1 and supplied to the receiving circuit 120, whereupon the audio signal Sr is derived and supplied to the telephone receiver 121.
On the other hand, audio signal St from the telephone transmitter 111 is supplied to the transmitting circuit 110, so as to be converted into the FM signal Su of the up channel and transmitted by way of the antenna 100 to the base unit 2.
The signal Su is received by antenna 200 of the base unit 2 and supplied to receiving circuit 220, whereupon the signal St is generated. This signal St is supplied to the telephone line network 3 via the converting circuit 261 and the switch circuit 262, and is then transmitted to the telephone set of the other party.
As shown in FIG. 6, if the talk key 132 of the handset unit 1 is depressed, so as to indicate the completion of the telephone conversation, the command signal CMND whose control code CTRL indicates the termination of the telephone conversation is generated and transmitted to the base unit 2 on the FM signal Su of the up channel.
The receiving circuit 220 of the base unit 2 derives this command signal CMND and supplies the same to the microcomputer 240 which, in turn, determines that the telephone communication is finished. As a result, the transmitting circuit 210 is inhibited from transmitting and the receiving circuit 220 is placed in the standby mode in which it repeatedly scans all up channels. The switch circuit 262 is placed in the on hook mode.
Also in the handset unit 1, after the command signal CMND whose control code CTRL indicates the end of the telephone conversation has been transmitted, the transmitting circuit 110 is inhibited from transmitting and the receiving circuit 120 is placed in the standby mode in which it alternately and intermittently receives the down third and seventh channels.
An incoming call to the handset unit 1 from the external line 3 is received by the handset unit 1 according to a connection sequence as, for example, shown in FIG. 5.
More specifically, when an incoming call arrives through the telephone line network 3, the associated ring tone signal is detected by the detecting circuit 264, whereupon a detection signal is generated and supplied to the microcomputer 240 in the base unit 2. The receiving circuit 220 is set to receive a vacant channel from among those indicated by the channel data CHDT stored in RAM 242, that is, either the up third channel or seventh channel. For example, if the third channel is vacant, the reception channel of the receiving circuit 220 is fixed to the up third channel. Further, the transmitting circuit 210 is permitted to transmit in the down third channel. As a result, the base unit 2 is set in the talk mode in the third channel.
The command signal CMND, whose control code CTRL indicates a request of the incoming call, is then repeatedly supplied to the transmitting circuit 210 from the microcomputer 240, whereupon the command signal CMND is converted into an FM signal Sd of the down third channel and transmitted to the handset unit 1.
The signal Sd is received by the antenna 100 of the handset unit 1. Meanwhile the receiving circuit 120 alternately and intermittently scans repeatedly the down third and seventh channels in accordance with the channel data CHDT stored in the RAM 142. However, when the reception channel becomes the third channel, the receiving circuit 120 senses the signal Sd and, as a result, generates the detection signal SQLC. The scanning operation of the receiving circuit 120 is then stopped at the third channel, whereupon the receiving circuit 120 demodulates the FM signal Sd to provide the command signal CMND. A determination is then performed on whether or not the system identifying code SYID in this command signal CMND coincides with the system identifying code SYID stored in the ROM 141.
In this case, since the system identifying codes SYID are coincident with each other and the control code CTRL in the command signal CMND indicates the request of the incoming call, the transmitting circuit 110 is permitted to transmit in the corresponding channel in which the FM signal Su is received, that is, the up third channel. Therefore, the handset unit 1 is also set in the talk mode in the third channel.
The command signal CMND which answers the request of the incoming call is then supplied to the transmitting circuit 110 from the microcomputer 140, whereupon this command signal CMND is converted into the FM signal Su of the up third channel and transmitted to the base unit 2.
When the FM signal Su, which is transmitted from the handset unit 1 via the up third channel is received by the base unit 2, the command signal CMND is generated by the receiving circuit 220 and supplied to the microcomputer 240.
Since the system identifying code SYID in the command signal CMND is coincident with the system identifying code SYID stored in the ROM 241 and the control code CTRL in the command signal CMND indicates the answer to the request of the incoming call, the transmitting circuit 210 and the receiving circuit 220 are set in the talk mode in the third channel.
Accordingly, the handset unit 1 and the base unit 2 is established via the third channel.
Further, in the handset unit 1, the oscillation circuit 138, which is controlled by the microcomputer 140, generates a ringer signal. This ringer signal is supplied to the speaker 139 so as to cause the speaker 139 to produce a bell sound, thus announcing the arrival of the incoming call.
If the talk key 132 in the handset unit 1 is depressed so as to answer the incoming call, an answer command signal CMND whose control code CTRL indicates the depression of the talk key 132 is generated. This command signal CMND is converted to the FM Signal Su and transmitted in a manner as previously described. Further, the oscillation circuit 138 is turned OFF, thus turning off the ringer.
The transmitted signal Su from the handset unit 1 is received by the base unit 2 and demodulated to form the command signal CMND in a manner as previously described. As a result, the switch circuit 262 is placed in the off hook state so that a communication channel is opened between the handset unit 1 and the base unit 2, thus enabling telephone communication between the handset unit 1 and the called phone.
Further, the user can make an outgoing call, receive an incoming call and end a telephone conversation by the use of the dial key 231, the hook switch 232, the transmitter and receiver 211 and 221, respectively, the oscillation circuit 238 and the speaker 239 of the base unit 2, in a manner similar to that used in a standard telephone set. At this time, a communication channel is not opened between the base unit 2 and the handset unit 1.
The cordless telephone in which the base unit 2 is provided with the transmitter 211 and the receiver 221 may further include a hold function. As a result, when a telephone conversation is performed utilizing the handset unit 1, the handset unit 1 may be set in a hold mode and after a predetermined period of time, the base unit 2 releases the hold mode, whereby the telephone conversation may be resumed through the use of the transmitter 211 and the receiver 221.
In order that the handset unit 1 and the base unit 2 can be easily placed in the hold mode and released therefrom, the communication channel between the handset unit 1 and the base unit 2 must be kept open during the hold mode. This insures that a hold releasing command signal CMND can be accessed between the handset unit 1 and the base unit 2.
Typically, during a telephone conversation, the user holds the handset unit 1 in his or her hand in a manner such that the antenna of the handset unit 1 stands in a relatively upright position. When the user places the handset unit 1 in a hold mode, the user may place the handset unit 1 horizontally on a table or the like, whereupon the antenna of the handset unit 1 is also placed in a horizontal direction. As a result, the propagation of radio waves is hindered depending on the material of the table or the like. Thus, when the handset unit 1 is placed in a hold mode, the radio waves (that is, the FM signal Su) transmitted by the handset unit 1 and the radio waves (that is, the FM signal Sd) received by the handset unit 1 are in a deteriorated condition.
Accordingly, the base unit 2 may fail to receive a hold release command CMND and, as a result, the handset unit 1 will remain in the hold mode until the user switches the talk key 132 of the handset unit 1 to the standby mode, thereby consuming a relatively large amount of power from the battery 151.